State-of-the-art Transmission Electron Microscopy (TEM) is based on high-brightness electron beams with beam energies typically in the range 100-300 keV. The beam energy is provided by a high-voltage (100-300 kV) electrostatic accelerator. The use of such high-voltage power supplies is cumbersome and expensive, in particular because of the requirement of an energy spread less than 1 eV, i.e. a relative energy stability of the order of 1 ppm. For applications such as Electron Energy Loss Spectroscopy (EELS) much smaller energy spreads are desired (0.01 eV or less), which at present can only be realized by using expensive energy filters and simultaneously sacrificing a substantial part of the beam current.
An attractive alternative to high-voltage electrostatic acceleration in terms of complexity and costs is acceleration by means of time-dependent fields in resonant radiofrequency (RF) cavities, as is common in relativistic particle accelerators. However, due to the limited power stability of high-power RF amplifiers, RF acceleration can provide relative energy stabilities of 10−4 at best.